Printers (argh)

I love HP printers but for god's sake, can't they just keep the reference numbers on the replacement ink cartridges the same??? I picked up a replacement cartridge that I thought was the same (instead of using the part # on the cartridge itself I was forced to try & remember what type of printer I had) and it's not quite the same. It looks identical except for some of the little spots on the copper part that (I guess) is the important bit. crap. now I've got to go exchange it...